Light emitting layer-forming solid material, organic electroluminescent device and method for producing the same

ABSTRACT

A light emitting layer-forming solid material including at least one host material and at least one light-emitting material, wherein the light emitting layer-forming solid material is used for forming a white light emitting layer having a single layer structure by an evaporation method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting layer-forming solidmaterial, an organic electroluminescent device (hereinafter may bereferred to as “organic electroluminescence device” or “organic ELdevice”) and a method for producing the organic electroluminescentdevice.

2. Description of the Related Art

Conventionally, in formation of a white light emitting layer having asingle layer structure, the dopant concentration must be controlled tobe 1% by mass or less, and thus, a large-scale production of the whitelight emitting layer cannot be attained by a generally usedco-evaporation method (see U.S. Pat. No. 5,683,823 and Japanese PatentApplication Laid-Open (JP-A) No. 2004-228088).

Then, JP-A No. 2004-228088 discloses a method for producing a whitelight emitting layer by combining a plurality of light emitting layersformed from the corresponding light emitting layer-forming solidmaterials. As compared to the co-evaporation method, the layer formationis improved by this method. Nevertheless, this method requires separatesolid materials corresponding to the light emitting layers, and alsorequires separate evaporation cells. As a result, the evaporation systembecomes complicated and a time-consuming step is required in which thecells are filled with the materials.

In addition, an evaporation film formed from a pellet of severalmaterials mixed may have a different composition from that beingexpected, since the materials have different sublimation temperatures.This problem has not yet been addressed by prior arts, and thecompositions of solid materials have not yet been designedsatisfactorily. Especially when powders of phosphorescent light-emittingmaterials (serving as light-emitting materials) are co-evaporated,device characteristics are not stable due to water or oxygen adsorbed onthe surfaces of the powders, which is problematic.

Furthermore, JP-A No. 2003-249359 discloses that an organiclight-emitting material and a thermally conductive material arepelletized into a solid. However, this literature has no descriptionabout the use of a phosphorescent light-emitting material as the organiclight-emitting material. According to Examples thereof, a green-lightemitting material Alq is used, and a white light-emitting layer having asingle layer structure cannot be formed through evaporation of only onetype of solid material.

Therefore, at present, keen demand has arisen for a light emittinglayer-forming solid material, an organic electroluminescent device and amethod for producing the organic electroluminescent device in which theheating temperature for the evaporation source (evaporation celltemperature) is changed while using only one type of light emittinglayer-forming solid material, thereby controlling the composition of theresultant evaporation film, requiring no difficult-to-controlco-evaporation, reducing variation in device performances and improvingrepetitive reproducibility.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a light emittinglayer-forming solid material, an organic electroluminescent device and amethod for producing the organic electroluminescent device in which theheating temperature of the evaporation source (evaporation celltemperature) is changed while using one type of light emittinglayer-forming solid material, thereby controlling the composition of theresultant evaporation film, requiring no difficult-to-controlco-evaporation, reducing variation in device performances and improvingrepetitive reproducibility.

The present inventor conducted extensive studies to solve the aboveexisting problems, and has found that the heating temperature of theevaporation source (evaporation cell temperature) is changed while usingone type of light emitting layer-forming solid material, therebycontrolling the composition of the resultant evaporation film, requiringno difficult-to-control co-evaporation, reducing variation in deviceperformances and improving repetitive reproducibility.

Also, according to another finding obtained by the present inventor,advantageous effects obtained when a phosphorescent light-emittingmaterial is formed into a solid material are greater than those obtainedwhen a fluorescent light-emitting material is formed into a solidmaterial. One reason for this is that a solid material has a smallersurface area than that of powder and thus is not easily affected bywater or oxygen. Another reason is that the phosphorescentlight-emitting material is more susceptible to water or oxygen than thefluorescent light-emitting material. Specifically, the solidphosphorescent light-emitting material exhibits greater effects ofimproving device characteristics (emission efficiency and service life)as compared with the solid fluorescent light-emitting material, sinceadsorption of water or oxygen can be reduced on the surface of thephosphorescent light-emitting material.

Furthermore, the present inventor has found that addition of a thermallyconductive material to the light emitting layer-forming solid materialeffectively suppresses generation of static electrical charges by virtueof electrical conductivity of the thermally conductive material, tothereby prevent adsorption of dust and impurities due to staticelectrical charges.

In the present invention, the amount by mass of the light emittinglayer-forming solid material is adjusted considering sublimationproperties of the materials, so that a white light emitting layer havinga single layer structure and a desired composition can be obtained at adesired evaporation rate. Moreover, the present inventor has found thatthe heating temperature of the heating source is adjusted to variablycontrol the composition of a light emitting layer having a single layerstructure, whereby the emission spectrum can be changed to control colortemperature and color rendering properties.

The present invention is based on the above findings obtained by thepresent inventor. Means for solving the above existing problems are asfollows.

<1> A light emitting layer-forming solid material, including:

at least one host material, and

at least one light-emitting material,

wherein the light emitting layer-forming solid material is used forforming a white light emitting layer having a single layer structure byan evaporation method.

<2> The light emitting layer-forming solid material according to <1>,wherein the at least one light-emitting material is at least twolight-emitting materials.

<3> The light emitting layer-forming solid material according to <2>,wherein the at least two light-emitting materials emit different lights.

<4> The light emitting layer-forming solid material according to any oneof <1> to <3>, wherein the at least one light-emitting material is aphosphorescent light-emitting material.

<5> The light emitting layer-forming solid material according to any oneof <1> to <4>, wherein a difference between a sublimation temperature ofthe host material and a sublimation temperature of the light-emittingmaterial is within 20° C. as an absolute value.

<6> The light emitting layer-forming solid material according to any oneof <1> to <5>, wherein a difference between a sublimation temperature ofthe host material and a sublimation temperature of the light-emittingmaterial is within 10° C. as an absolute value.

<7> The light emitting layer-forming solid material according to any oneof <1> to <6>, further including at least one thermally conductivematerial having no sublimation property, and thermal conductivity of thethermally conductive material is higher than that of the other materialscontained in the light emitting layer-forming solid material.

<8> The light emitting layer-forming solid material according to any oneof <1> to <7>, wherein the light emitting layer-forming solid materialis used as an evaporation source to form an evaporation film, and acomposition of the evaporation film is changed depending on a heatingtemperature of the evaporation source.

<9> The light emitting layer-forming solid material according to <8>,wherein the composition of the evaporation film is adjusted bycontrolling the heating temperature of the evaporation source.

<10> The light emitting layer-forming solid material according to anyone of <1> to <9>, wherein the light emitting layer-forming solidmaterial is evaporated to form an evaporation film whose composition isdifferent from a composition of the light emitting layer-forming solidmaterial.

<11> A method for producing an organic electroluminescent device,including:

evaporating a light emitting layer-forming solid material according toany one of <1> to <10> so as to form a light emitting layer.

<12> An organic electroluminescent device obtained by the methodaccording to <11>.

The present invention can provide a light emitting layer-forming solidmaterial, an organic electroluminescent device and a method forproducing the organic electroluminescent device in which the heatingtemperature of the evaporation source is changed while using one type oflight emitting layer-forming solid material, thereby controlling thecomposition of the resultant evaporation film, requiring nodifficult-to-control co-evaporation, reducing variation in deviceperformances and improving repetitive reproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one exemplary organic electroluminescentdevice of the present invention.

DETAILED DESCRIPTION OF THE INVENTION (Light Emitting Layer-FormingSolid Material)

A light emitting layer-forming solid material of the present inventionis a solid material used for forming a white light emitting layer havinga single layer structure by an evaporation method, and includes at leastone host material and at least one light-emitting material; and, ifnecessary, further includes a thermally conductive material and othercomponents.

<Host Material>

The host material is not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof includehole transporting host materials having excellent hole transportingproperties and electron transporting host materials having excellentelectron transporting properties.

—Hole Transporting Host Material—

The hole transporting host material is not particularly limited and maybe appropriately selected depending on the intended purpose. Examples ofthe hole transporting host material include pyrrole, indole, carbazole,azaindole, azacarbazole, pyrazole, imidazole, polyarylalkane,pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substitutedchalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane,aromatic tertiary amine compounds, styrylamine compounds, aromaticdimethylidine compounds, porphyrin compounds, polysilane compounds,poly(N-vinylcarbazole), aniline copolymers, conductivehigh-molecular-weight oligomers (e.g., thiophene oligomers andpolythiophenes), organic silanes, carbon films and derivatives thereof.

Among them, preferred are indole derivatives, carbazole derivatives,azaindole derivatives, azacarbazole derivatives, aromatic tertiary aminecompounds and thiophene derivatives. More preferred are compoundshaving, in their molecule, an indole skeleton, a carbazole skeleton, anazaindole skeleton, an azacarbazole skeleton or an aromatic tertiaryamine skeleton. Particularly preferred are compound having a carbazoleskeleton in their molecule.

Also, in the present invention, host materials part or all of thehydrogen atoms of which have been substituted by deuterium may be used(JP-A Nos. 2009-277790 and 2004-515506).

Specific examples of the hole transporting host material include thefollowing compounds, but employable hole transporting host materials arenot limited thereto.

The amount of the hole transporting host material contained in the lightemitting layer-forming solid material is preferably 10% by mass to 99.9%by mass, more preferably 20% by mass to 99.5% by mass, still morepreferably 30% by mass to 99% by mass.

—Electron Transporting Host Material—

The electron transporting host material is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples thereof include pyridine, pyrimidine, triazine, imidazole,pyrazole, triazole, oxazole, oxadiazole, fluorenone,anthraquinodimethane, anthrone, diphenylquinone, thiopyrandioxide,carbodiimide, fluorenylidenemethane, distyrylpyradine,fluorine-substituted aromatic compounds, heterocyclic tetracarboxylicanhydrides (e.g., naphthalene and perylene), phthalocyanine, derivativesthereof (which may form a condensed ring with another ring) and variousmetal complexes such as metal complexes of 8-quinolynol derivatives,metal phthalocyanine, and metal complexes having benzoxazole orbenzothiazole as a ligand.

Further examples of the electron transporting host material includemetal complexes, azole derivatives (e.g., benzimidazole derivatives andimidazopyridine derivatives) and azine derivatives (e.g., pyridinederivatives, pyrimidine derivatives and triazine derivatives). Amongthem, in the present invention, metal complex compounds are preferred interms of durability. The metal complex compounds are more preferablymetal complexes containing a ligand which has at least one nitrogenatom, oxygen atom, or sulfur atom and which is coordinated with themetal.

The metal ion contained in the metal complexes is not particularlylimited and may be appropriately selected depending on the intendedpurpose. It is preferably a beryllium ion, a magnesium ion, an aluminumion, a gallium ion, a zinc ion, an indium ion, a tin ion, a platinum ionor a palladium ion; more preferably a beryllium ion, an aluminum ion, agallium ion, a zinc ion, a platinum ion or a palladium ion; particularlypreferably an aluminum ion, a zinc ion or a palladium ion.

The ligand contained in the metal complexes is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include those described in, for example,“Photochemistry and Photophysics of Coordination Compounds” authored byH. Yersin, published by Springer-Verlag Company in 1987; and “YUHKIKINZO KUKAGAKU—KISO TO OUYOU—(Metalorganic Chemistry—Fundamental andApplication—)” authored by Akio Yamamoto, published by ShokaboPublishing Co., Ltd. in 1982.

The ligand is, for example, nitrogen-containing heterocyclic ligands(preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbonatoms, particularly preferably 3 to 15 carbon atoms). It may be aunidentate ligand or a bi- or higher-dentate ligand. Preferred are bi-to hexa-dentate ligands, and mixed ligands of bi- to hexa-dentateligands with a unidentate ligand.

Examples of the ligand include azine ligands (e.g., pyridine ligands,bipyridyl ligands and terpyridine ligands); hydroxyphenylazole ligands(e.g., hydroxyphenylbenzoimidazole ligands, hydroxyphenylbenzoxazoleligands, hydroxyphenylimidazole ligands and hydroxyphenylimidazopyridineligands) alkoxy ligands (those having preferably 1 to 30 carbon atoms,more preferably 1 to 20 carbon atoms, particularly preferably 1 to 10carbon atoms, such as methoxy, ethoxy, butoxy and 2-ethylhexyloxy); andaryloxy ligands (those having preferably 6 to 30 carbon atoms, morepreferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbonatoms, such as phenyloxy, 1-naphthyloxy, 2-naphthyloxy,2,4,6-trimethylphenyloxy and 4-biphenyloxy), heteroaryloxy ligands(those having preferably 1 to 30 carbon atoms, more preferably 1 to 20carbon atoms, particularly preferably 1 to 12 carbon atoms, examples ofwhich include pyridyloxy, pyrazyloxy, pyrimidyloxy and quinolyloxy);alkylthio ligands (those having preferably 1 to 30 carbon atoms, morepreferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbonatoms, examples of which include methylthio and ethylthio); arylthioligands (those having preferably 6 to 30 carbon atoms, more preferably 6to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms,examples of which include phenylthio); heteroarylthio ligands (thosehaving preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbonatoms, particularly preferably 1 to 12 carbon atoms, examples of whichinclude pyridylthio, 2-benzimidazolylthio, 2-benzoxazolylthio and2-benzothiazolylthio); siloxy ligands (those having preferably 1 to 30carbon atoms, more preferably 3 to 25 carbon atoms, particularlypreferably 6 to 20 carbon atoms, examples of which include atriphenylsiloxy group, a triethoxysiloxy group and a triisopropylsiloxygroup); aromatic hydrocarbon anion ligands (those having preferably 6 to30 carbon atoms, more preferably 6 to 25 carbon atoms, particularlypreferably 6 to 20 carbon atoms, examples of which include a phenylanion, a naphthyl anion and an anthranyl anion); aromatic heterocyclicanion ligands (those having preferably 1 to 30 carbon atoms, morepreferably 2 to 25 carbon atoms, particularly preferably 2 to 20 carbonatoms, examples of which include a pyrrole anion, a pyrazole anion, atriazole anion, an oxazole anion, a benzoxazole anion, a thiazole anion,a benzothiazole anion, a thiophene anion and a benzothiophene anion);and indolenine anion ligands. Among them, nitrogen-containingheterocyclic ligands, aryloxy ligands, heteroaryloxy groups, siloxyligands, etc. are more preferred, and nitrogen-containing heterocyclicligands, aryloxy ligands, siloxy ligands, aromatic hydrocarbon anionligands, aromatic heterocyclic anion ligands, etc. are still morepreferred.

The metal complexes used for the electron transporting host material arecompounds described in, for example, JP-A Nos. 2002-235076, 2004-214179,2004-221062, 2004-221065, 2004-221068 and 2004-327313.

Specific examples of the electron transporting host material include thefollowing materials, but employable electron transporting host materialsare not limited thereto.

The amount of the electron transporting host material is preferably 10%by mass to 99.9% by mass, more preferably 20% by mass to 99.5% by mass,still more preferably 30% by mass to 99% by mass, relative to the totalamount of the light emitting layer-forming solid material.

<Light-Emitting Material>

The light-emitting material may be any of a phosphorescentlight-emitting material and a fluorescent light-emitting material. Thephosphorescent light-emitting material is preferable as compared withthe fluorescent light-emitting material, since the phosphorescentlight-emitting material exhibits higher light-emission efficiency. Inaddition, when the phosphorescent light-emitting material, which is moresusceptible to water or oxygen than in the fluorescent light-emittingmaterial, is formed into a solid, adverse effects caused by water oroxygen from the outside can be minimalized. The resultant phosphorescentlight-emitting material in solid form has improved performances(light-emission efficiency and service life) as compared withconventional phosphorescent light-emitting materials in powder form,which is particularly preferred.

Examples of the light-emitting material include (1) a material emittingwhite light by itself through association emission and (2) a materialcontaining at least two light-emitting materials emitting lights ofdifferent colors.

—(1) Material Emitting White Light by Itself Through AssociationEmission—

The material emitting white light by itself through association emissionis preferably a phosphorescent light-emitting material, more preferablya platinum complex.

Examples of the ligand of the platinum complex include those describedin, for example, “Comprehensive Coordination Chemistry” authored by G.Wilkinson et al., published by Pergamon Press Company in 1987;“Photochemistry and Photophysics of Coordination Compounds” authored byH. Yersin, published by Springer-Verlag Company in 1987; and “YUHKIKINZO KUKAGAKU—KISO TO OUYOU—(Metalorganic Chemistry—Fundamental andApplication—)” authored by Akio Yamamoto, published by ShokaboPublishing Co., Ltd. in 1982.

Specific examples of the ligand include halogen ligands (preferably,chlorine ligand); aromatic carbon ring ligands such as cyclopentadienylanion, benzene anion and naphthyl anion; nitrogen-containing heterocyclic ligands such as phenyl pyridine, benzoquinoline, quinolinol,bipyridyl and phenanthrorine); diketone ligands such as acetyl acetone;carboxylic acid ligands such as acetic acid ligand; alcoholate ligandssuch as phenolate ligand; carbon monoxide ligand; isonitrile ligand; andcyano ligand, with nitrogen-containing hetero cyclic ligands beingparticularly preferred.

The above-described complexes may be a complex containing one transitionmetal atom in the compound, or a so-called polynuclear complexcontaining two or more transition metal atoms. In the latter case, thecomplexes may contain different metal atoms at the same time. Specificexamples of the phosphorescent light-emitting material include thefollowing materials, but employable phosphorescent light-emittingmaterials are not limited thereto.

The concentration of the platinum complex (dopant) is preferably 10% bymass to 90% by mass, more preferably 20% by mass to 60% by mass, stillmore preferably 30% by mass to 50% by mass, relative to the hostmaterial.

—(2) Material Containing at Least Two Light-Emitting Materials EmittingLights of Different Colors—

The material containing at least two light-emitting materials emittinglights of different colors is preferably a mixture containinglight-emitting materials emitting lights of several colors for emittingwhite light, more preferably a mixture of light-emitting materialsemitting lights of three different colors of red (R), green (G) and blue(B).

The light-emitting material contained in the material (2) may be any ofthe phosphorescent light-emitting material and the fluorescentlight-emitting material, with the phosphorescent light-emitting materialbeing particularly preferred.

—Phosphorescent Light-Emitting Material—

The phosphorescent light-emitting material is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include complexes containing a transition metal atom ora lanthanoid atom.

Examples of the transition metal atom include ruthenium, rhodium,palladium, tungsten, rhenium, osmium, iridium and platinum, withrhenium, iridium, platinum and iridium being particularly preferred.

Examples of the ligand include those described in, for example,“Comprehensive Coordination Chemistry” authored by G. Wilkinson et al.,published by Pergamon Press Company in 1987; “Photochemistry andPhotophysics of Coordination Compounds” authored by H. Yersin, publishedby Springer-Verlag Company in 1987; and “YUHKI KINZO KUKAGAKU—KISO TOOUYOU—(Metalorganic Chemistry—Fundamental and Application—)” authored byAkio Yamamoto, published by Shokabo Publishing Co., Ltd. in 1982.

Specific examples of the ligand include halogen ligands (preferably,chlorine ligand); aromatic carbon ring ligands such as cyclopentadienylanion, benzene anion and naphthyl anion; nitrogen-containing heterocyclic ligands such as phenyl pyridine, benzoquinoline, quinolinol,bipyridyl and phenanthrorine); diketone ligands such as acetyl acetone;carboxylic acid ligands such as acetic acid ligand; alcoholate ligandssuch as phenolate ligand; carbon monoxide ligand; isonitrile ligand; andcyano ligand, with nitrogen-containing hetero cyclic ligands beingparticularly preferred.

The above-described complexes may be a complex containing one transitionmetal atom in the compound, or a so-called polynuclear complexcontaining two or more transition metal atoms. In the latter case, thecomplexes may contain different metal atoms at the same time. Specificexamples of the phosphorescent light-emitting material include thefollowing materials, but employable phosphorescent light-emittingmaterials are not limited thereto.

The Ir-containing complex as the phosphorescent light-emitting materialis not particularly limited and may be appropriately selected dependingon the intended purpose. Preferred are compounds represented by thefollowing General Formulas (1), (2) and (3).

In General Formulas (1), (2) and (3), n is an integer of 1 to 3, X—Ydenotes a bidentate ligand, A denotes a ring structure which may containa nitrogen atom, a sulfur atom or an oxygen atom, R¹¹ represents asubstituent, m1 is an integer of 0 to 6, when m1 is 2 or greater, theadjacent R¹¹s may be bonded to form a ring which may contain a nitrogenatom, a sulfur atom or an oxygen atom and which may have a substituent,R¹² represents a substituent, m2 is an integer of 0 to 4, when m2 is 2or greater, the adjacent R¹²s may be bonded to form a ring which maycontain a nitrogen atom, a sulfur atom or an oxygen atom and which mayhave a substituent, and R¹¹ and R¹² may be bonded to form a ring whichmay contain a nitrogen atom, a sulfur atom or an oxygen atom and whichmay have a substituent.

The ring A denotes a ring structure which may contain a nitrogen atom, asulfur atom or an oxygen atom. Preferred examples of the ring structureinclude 5-membered and 6-membered rings. The ring may have asubstituent.

X—Y denotes a bidentate ligand. Preferred examples thereof includebidentate monoanion ligands.

Examples of the bidentate monoanion ligands include picolinate (pic),acetylacetonato (acac) and dipyvaloylmethanato (t-butyl acac).

Examples of other ligands than the above ligands include ligandsdescribed on pp. 89 to 91 of International Publication No. WO2002/15645by Lamansky, et al.

The substituent represented by R¹¹ or R¹² is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include a halogen atom, an alkoxy group, an aminogroup, an alkyl group, a cycloalkyl group, an aryl group which maycontain a nitrogen atom or a sulfur atom, an aryloxy group which maycontain a nitrogen atom or a sulfur atom, each of the groups may furthercontain a substituent.

Regarding the groups represented by R¹¹ and R¹², the adjacent groups maybe bonded to form a ring which may contain a nitrogen atom, a sulfuratom or an oxygen atom. Preferred examples of the ring include5-membered and 6-membered rings. The ring may have a substituent.

Specific examples of the compounds represented by General Formulas (1),(2) and (3) include the following compounds, but employablephosphorescent light-emitting materials are not limited thereto.

Further examples of the phosphorescent light-emitting material includethe following compounds.

The total amount of the phosphorescent light-emitting material ispreferably 0.5% by mass to 30% by mass, more preferably 0.5% by mass to20% by mass, still more preferably 3% by mass to 10% by mass, relativeto the total amount of the light emitting layer-forming solid material.

—Fluorescent Light-Emitting Material—

The fluorescent light-emitting material is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples thereof include benzoxazole, benzimidazole, benzothiazole,styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene,naphthalimide, coumarin, pyran, perinone, oxadiazole, aldazine,pyralidine, cyclopentadiene, styrylamine, aromatic dimethylidynecompounds, condensed polycyclic aromatic compounds (e.g., anthracene,phenanthroline, pyrene, perylene, rubrene and pentacene), various metalcomplexes (e.g., metal complexes of 8-quinolinol, pyrromethene complexesand rare-earth complexes), polymer compounds (e.g., polythiophene,polyphenylene and polyphenylenevinylene), organic silanes andderivatives thereof.

Specific examples of the fluorescent light-emitting material include thefollowing compounds, but employable fluorescent light-emitting materialsare not limited thereto.

The total amount of the fluorescent light-emitting material ispreferably 0.1% by mass to 30% by mass, more preferably 0.2% by mass to15% by mass, further preferably 0.5% by mass to 12% by mass, relative tothe total amount of the light emitting layer-forming solid material.

The difference between the sublimation temperature of the host materialand the sublimation temperature of the light-emitting material ispreferably within 20° C., more preferably within 10° C. When thedifference between the sublimation temperature of the host material andthe sublimation temperature of the light-emitting material is greaterthan 20° C. as an absolute value, a small change in heating temperatureof the evaporation source greatly changes the composition of theresultant film, potentially leading to large variation in devicecharacteristics.

Here, the sublimation temperature refers to a temperature at which themass of a substance is decreased by 10% by mass when measured in vacuumthrough TG-DTA.

Here, the heating temperature of the evaporation source refers to atemperature that is the same as the temperature of the evaporation cell.

—Thermally Conductive Material

The light emitting layer-forming solid material preferably contains atleast one thermally conductive material having no sublimation property,since the light emitting layer-forming solid material can be uniformlyheated to suppress thermodecomposition of the materials due to localheating.

The thermally conductive material is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include thermally-conductive carbides, nitrides and metals.Specific examples thereof include SiC, diamond, tungsten, Cu, graphite,BN, AlN, WC and TiC, with SiC being particularly preferred.

The amount of the thermally conductive material having no sublimationproperty is preferably 10% by mass to 90% by mass relative to the totalamount of the light emitting layer-forming solid material.

If necessary, the light emitting layer-forming solid material maycontain a binder to ensure its moldability and strength.

The binder is preferably selected from materials that are not sublimateor vaporize at the evaporation temperature applied. Specific examplesthereof include epoxy resins, urethane resins and acryl resins.

The method for producing the light emitting layer-forming solid materialis not particularly limited and may be appropriately selected dependingon the intended purpose. In one exemplary method, the host material, thelight-emitting material and the thermally conductive material having nosublimation property are added at a desired ratio to and thoroughlystirred with a mixer until a homogeneous mixture is obtained. Theresultant mixture is completely dehydrated with heating at 60° C. to 80°C. in vacuum, and then is charged into a compression molding apparatusin an inert gas atmosphere or in vacuum, followed by hot-press moldingat a pressure of 50 kg/cm² to 200 kg/cm² and a heating temperature of100° C. to 250° C.

The composition of an evaporation film formed from the light emittinglayer-forming solid material preferably changes depending on the heatingtemperature of the evaporation source. The composition of theevaporation film is desirably adjusted by desirably controlling thetemperature of the evaporation source. Specifically, the heatingtemperature of the evaporation source is preferably 100° C. to 400° C.

(Method for Producing Organic Electroluminescent Device)

A method of the present invention for producing an organicelectroluminescent device (organic electroluminescent device-producingmethod) includes at least a light emitting layer-forming step; and, ifnecessary, further includes other steps.

<Light Emitting Layer-Forming Step>

The light emitting layer-forming step is a step of evaporating the lightemitting layer-forming solid material of the present invention so as toform a light emitting layer.

The vacuum evaporation conditions, including evaporation rate,evaporation pressure, heating temperature of an evaporation source, typeof an evaporation source container, substrate temperature, evaporationsource-substrate interdistance, angle formed between substrate surfaceand straight line connecting evaporation source with substrate surfaceand degree of vacuum upon evaporation, are not particularly limited andmay be appropriately selected depending on the intended purpose.

Suitably employed evaporation source containers are, for example, analumina crucible, a quartz cell and a metal board made of Mo, W, etc.

The heating temperature of the evaporation source may be appropriatelyselected depending on the material for the light emitting layer, butpreferably 100° C. to 400° C. The heating temperature of the evaporationsource refers to a temperature that is the same as the temperature ofthe evaporation cell.

The substrate temperature is preferably −50° C. to 100° C.

The evaporation source-substrate interdistance is preferably 5 cm to 70cm.

The angle formed between the perpendicular line to the substrate surfaceand the straight line connecting the evaporation source with thesubstrate surface is preferably 0° to 40°.

The degree of vacuum upon evaporation is preferably 1×10⁻⁵ Pato 5×10⁻⁴Pa.

The evaporation rate is preferably 0.01 nm/s to 10 nm/s, more preferably0.1 nm/s to 1 nm/s. When two or more types of the light emittinglayer-forming solid material are co-evaporated at different evaporationrates, the evaporation rate is the total evaporation rate of theseevaporation rates.

At the light emitting layer-forming step, in order to improve thermalcontact between the evaporation cell and the light emittinglayer⁻forming solid material, a highly thermally conductive,non⁻sublimation material is optionally charged into the evaporation celltogether with the solid material.

The thermally conductive material is not particularly limited and may beappropriately selected depending on the intended purpose. Suitablyemployed examples thereof include particles of thermally conductivecarbides, nitrides and metals such as SiC, diamond, tungsten, Cu,graphite, BN, AlN, WC and TiC.

Notably, the layers constituting the organic electroluminescent deviceother than the light emitting layer (e.g., a hole injection layer andelectron injection layer) can be produced using a solid material.

(Organic Electroluminescent Device)

An organic electroluminescent device of the present invention isproduced by the organic electroluminescent device-producing method ofthe present invention. The organic electroluminescent device includes ananode, a cathode and at least a light emitting layer therebetween. Itpreferably contains an electron transport layer, an electron injectionlayer, a hole injection layer, a hole transport layer, a hole blockinglayer and an electron blocking layer; and, if necessary, may furtherinclude other components.

<Light Emitting Layer>

The light emitting layer is formed at the light emitting layer-formingstep.

The thickness of the light emitting layer is not particularly limitedand may be appropriately selected depending on the intended purpose. Thethickness thereof is preferably 5 nm to 100 nm, more preferably 20 nm to40 nm.

<Electron Injection Layer and Electron Transport Layer>

The electron injection layer or the electron transport layer is a layerhaving the function of receiving electrons from the cathode or from thecathode side and transporting the electrons to the anode side.

The electron transport layer contains the electron transporting hostmaterial, the electron-donating dopant and other materials.

The thickness of the electron injection layer or the electron transportlayer is not particularly limited and may be appropriately selecteddepending on the intended purpose. The thickness thereof is preferably500 nm or smaller from the viewpoint of reducing drive voltage.

The thickness of the electron transport layer is preferably 1 nm to 500nm, more preferably 5 nm to 200 nm, further preferably 10 nm to 100 nm.

The thickness of the electron injection layer is preferably 0.1 nm to200 nm, more preferably 0.2 nm to 100 nm, further preferably 0.5 nm to50 nm.

The electron injection layer or the electron transport layer may have asingle-layered structure made of one or more materials, or amulti-layered structure made of a plurality of layers which areidentical or different in composition.

<Hole Injection Layer and Hole Transport Layer>

The hole injection layer or the hole transport layer is a layer havingthe function of receiving holes from the anode or from the anode sideand transporting the holes to the cathode side. The hole injection layeror the hole transport layer may have a single-layered structure or amulti-layered structure made of a plurality of layers which areidentical or different in composition.

The hole injection material or the hole transport material used in theselayers may be any of a low-molecular-weight compound and ahigh-molecular-weight compound.

The hole injection material or the hole transport material is notparticularly limited and may be appropriately selected depending on theintended purpose. Examples thereof include pyrrole derivatives,carbazole derivatives, triazole derivatives, oxazole derivatives,oxadiazole derivatives, imidazole derivatives, polyarylalkanederivatives, pyrazoline derivatives, pyrazolone derivatives,phenylenediamine derivatives, arylamine derivatives, amino-substitutedchalcone derivatives, styrylanthracene derivatives, fluorenonederivatives, hydrazone derivatives, stilbene derivatives, silazanederivatives, aromatic tertiary amine compounds, styrylamine compounds,aromatic dimethylidine compounds, phthalocyanine compounds, porphyrincompounds, thiophene derivatives, organosilane derivatives and carbon.These may be use alone or in combination.

The hole injection layer or the hole transport layer may contain anelectron-accepting dopant.

The electron-accepting dopant may be, for example, an inorganic ororganic compound, so long as it has electron accepting property and thefunction of oxidizing an organic compound.

The inorganic compound is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include metal halides (e.g., ferric chloride, aluminum chloride,gallium chloride, indium chloride and antimony pentachloride) and metaloxides (e.g., vanadium pentaoxide and molybdenum trioxide).

The organic compound is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include compounds having a substituent such as a nitro group, ahalogen, a cyano group and a trifluoromethyl group; quinone compounds;acid anhydride compounds; and fullerenes. These electron-acceptingdopants may be used alone or in combination.

The amount of the electron-accepting dopant used varies depending on thetype of the material. The amount thereof is preferably 0.01% by mass to50% by mass, more preferably 0.05% by mass to 30% by mass, particularlypreferably 0.1% by mass to 30% by mass, relative to the hole transportmaterial or the hole injection material.

The hole injection layer or the hole transport layer is not particularlylimited and can be formed by a known method. Specifically, suitablyemployable methods include a dry film forming method such as asputtering method or an evaporation method, a wet coating method, atransfer method, a printing method and an inkjet method.

The thickness of the hole injection layer or the hole transport layer ispreferably 1 nm to 500 nm, more preferably 5 nm to 250 nm, furtherpreferably 10 nm to 200 nm.

<Hole Blocking Layer and Electron Blocking Layer>

The hole blocking layer is a layer having the function of preventing theholes, which have been transported from the anode side to the lightemitting layer, from passing toward the cathode side, and is generallyprovided as an organic compound layer adjacent to the light emittinglayer on the cathode side.

The electron blocking layer is a layer having the function of preventingthe electrons, which have been transported from the cathode side to thelight emitting layer, from passing toward the anode side, and isgenerally provided as an organic compound layer adjacent to the lightemitting layer on the anode side.

The compound for the hole blocking layer is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples thereof include aluminum complexes (e.g., BAlq), triazolederivatives and phenanthroline derivatives (e.g., BCP).

Examples of the compound employable for forming the electron blockinglayer include the above-described hole transport materials.

The electron blocking layer or the hole blocking layer is notparticularly limited and can be formed by a known method. Specifically,suitably employable methods include a dry film forming method such as asputtering method or an evaporation method, a wet coating method, atransfer method, a printing method and an inkjet method.

The thickness of the hole blocking layer or the electron blocking layeris preferably 1 nm to 200 nm, more preferably 1 nm to 50 nm, furtherpreferably 3 nm to 10 nm. Also, the hole blocking layer or the electronblocking layer may have a single-layered structure made of one or morematerials, or a multi-layered structure made of a plurality of layerswhich are identical or different in composition.

<Electrode>

The organic electroluminescence device of the present invention includespair of electrodes; i.e., an anode and a cathode. In terms of thefunction of the organic electroluminescence device, at least one of theanode and the cathode is preferably transparent. In general, the anodemay be any material, so long as it has the function of serving as anelectrode which supplies holes to the organic compound layer.

The shape, structure, size, etc. thereof are not particularly limitedand may be appropriately selected from known electrode materialsdepending on the intended application/purpose of the organicelectroluminescence device.

Preferred examples of the material for the electrodes include metals,alloys, metal oxides, conductive compounds and mixtures thereof.

—Anode—

The material for the anode is, for example, conductive metal oxides suchas tin oxides doped with, for example, antimony and fluorine (ATO andFTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO) andindium zinc oxide (IZO); metals such as gold, silver, chromium andnickel; mixtures or laminates of these metals and the conductive metaloxides; inorganic conductive materials such as copper iodide and coppersulfide; organic conductive materials such as polyaniline, polythiopheneand polypyrrole; and laminates of these materials and ITO. Among them,conductive metal oxides are preferred. In particular, ITO is preferredfrom the viewpoints of productivity, high conductivity, transparency,etc.

—Cathode—

The material for the cathode is, for example, alkali metals (e.g., Li,Na, K and Cs), alkaline earth metals (e.g., Mg and Ca), gold, silver,lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys,magnesium-silver alloys and rare earth metals (e.g., indium andytterbium). These may be used alone, but it is preferred that two ormore of them are used in combination from the viewpoint of satisfyingboth stability and electron-injection property.

Among them, as the materials for forming the cathode, alkali metals oralkaline earth metals are preferred in terms of excellentelectron-injection property, and materials containing aluminum as amajor component are preferred in terms of excellent storage stability.

The term “material containing aluminum as a major component” refers to amaterial composed of aluminum alone; alloys containing aluminum and0.01% by mass to 10% by mass of an alkali or alkaline earth metal; orthe mixtures thereof (e.g., lithium-aluminum alloys andmagnesium-aluminum alloys).

The method for forming the electrodes is not particularly limited andmay be a known method. Examples thereof include wet methods such asprinting methods and coating methods; physical methods such as vacuumdeposition methods, sputtering methods and ion plating methods; andchemical methods such as CVD and plasma CVD methods. The electrodes canbe formed on a substrate by a method appropriately selected from theabove methods in consideration of their suitability to the material forthe electrodes. For example, when ITO is used as the material for theanode, the anode may be formed in accordance with a DC or high-frequencysputtering method, a vacuum deposition method, or an ion plating method.For example, when a metal (or metals) is (are) selected as the material(or materials) for the cathode, one or more of them may be appliedsimultaneously or sequentially by, for example, a sputtering method.

Patterning for forming the electrodes may be performed by a chemicaletching method such as photolithography; a physical etching method suchas etching by laser; a method of vacuum deposition or sputtering using amask; a lift-off method; or a printing method.

<Substrate>

The organic electroluminescence device of the present invention ispreferably formed on a substrate, may be formed so that a substratecomes into direct contact with the electrodes, or may be formed on asubstrate by the mediation of an intermediate layer.

The material for the substrate is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include inorganic materials such as yttria-stabilized zirconia(YSZ) and glass (alkali-free glass and soda-lime glass); and organicmaterials such as polyesters (e.g., polyethylene terephthalate,polybutylene phthalate and polyethylene naphthalate), polystyrene,polycarbonate, polyether sulfone, polyarylate, polyimide,polycycloolefin, norbornene resins and poly(chlorotrifluoroethylene).

The shape, structure, size, etc. of the substrate are not particularlylimited and may be appropriately selected depending on, for example, theintended application/purpose of the light-emitting device. In general,the substrate is preferably a sheet. The substrate may have a single- ormulti-layered structure, and may be a single member or a combination oftwo or more members. The substrate may be opaque, colorless transparent,or colored transparent.

The substrate may be provided with a moisture permeation-preventinglayer (gas barrier layer) on the front or back surface thereof.

The moisture permeation-preventing layer (gas barrier layer) ispreferably made from an inorganic compound such as silicon nitride andsilicon oxide.

The moisture permeation-preventing layer (gas barrier layer) may beformed through, for example, high-frequency sputtering.

—Other Components—

The other components are not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include a protective layer, a sealing container, a resin seallayer and a sealing adhesive.

The type of the protective layer, the sealing container, the resin seallayer or the sealing adhesive is not particularly limited and may beappropriately selected depending on the intended purpose. Thedescription of JP-A No. 2009-152572 and other literatures can be appliedthereto.

FIG. 1 is a schematic view of one exemplary layer structure of theorganic electroluminescence device of the present invention. An organicelectroluminescence device 10 has a layer structure in which a glasssubstrate 1 and an anode 2 (e.g., an ITO electrode), a hole injectionlayer 3, a hole transport layer 4, a light emitting layer 5, a firstelectron transport layer 6, a second electron transport is layer 7, anelectron injection layer (not illustrated), a cathode 8 (e.g., an Al—Lielectrode) disposed on the glass substrate in this order. Notably, theanode 2 (e.g., the ITO electrode) and the cathode 8 (e.g., the Al—Lielectrode) are connected together via a power source.

—Driving—

The organic electroluminescence device can emit light when a DC voltage(which, if necessary, contains AC components) (generally 2 volts to 15volts) or a DC is applied to between the anode and the cathode.

The organic electroluminescence device of the present invention can beapplied to an active matrix using a thin film transistor (TFT). Anactive layer of the thin film transistor may be made from, for example,amorphous silicon, high-temperature polysilicon, low-temperaturepolysilicon, microcrystalline silicon, oxide semiconductor, organicsemiconductor and carbon nanotube.

The thin film transistor used for the organic electroluminescence deviceof the present invention may be those described in, for example,International Publication No. WO2005/088726, JP-A No. 2006-165529 andU.S. Pat. Application Publication No. 2008/0237598.

The organic electroluminescence device of the present invention is notparticularly limited. In the organic electroluminescence device, thelight-extraction efficiency can be further improved by various knownmethods. It is possible to increase the light-extraction efficiency toimprove the external quantum efficiency, for example, by processing thesurface shape of the substrate (for example, by forming a fineconcavo-convex pattern), by controlling the refractive index of thesubstrate, the ITO layer and/or the organic layer, or by controlling thethickness of the substrate, the ITO layer and/or the organic layer.

The manner in which light is extracted from the organicelectroluminescence device of the present invention may be top-emissionor bottom-emission.

The organic electroluminescence device may have a resonator structure.For example, in a first embodiment, on a transparent substrate arestacked a multi-layered film mirror composed of a plurality of laminatedfilms having different refractive indices, a transparent orsemi-transparent electrode, a light emitting layer and a metalelectrode. The light generated in the light emitting layer is repeatedlyreflected between the multi-layered film mirror and the metal electrode(which serve as reflection plates); i.e., is resonated.

In a second embodiment, a transparent or semi-transparent electrode anda metal electrode are stacked on a transparent substrate. In thisstructure, the light generated in the light emitting layer is repeatedlyreflected between the transparent or semi-transparent electrode and themetal electrode (which serve as reflection plates); i.e., is resonated.

For forming the resonance structure, an optical path length determinedbased on the effective refractive index of two reflection plates, and onthe refractive index and the thickness of each of the layers between thereflection plates is adjusted to be an optimal value for obtaining adesired resonance wavelength.

The calculation formula applied in the case of the first embodiment isdescribed in JP-A No. 09-180883.

The calculation formula in the case of the second embodiment isdescribed in JP-A No. 2004-127795.

—Application—

The application of the organic electroluminescence device of the presentinvention is not particularly limited and may be appropriately selecteddepending on the intended purpose. The organic electroluminescencedevice can be suitably used in, for example, display devices, displays,backlights, electrophotography, illuminating light sources, recordinglight sources, exposing light sources, reading light sources, markers,interior accessories and optical communication.

As a method for forming a full color-type display, there are known, forexample, as described in “Monthly Display,” September 2000, pp. 33 to37, a tricolor light emission method by arranging, on a substrate,organic electroluminescence devices corresponding to three primarycolors (blue color (B), green color (G) and red color (R)); a whitecolor method by separating white light emitted from an organicelectroluminescence device for white color emission into three primarycolors through a color filter; and a color conversion method byconverting a blue light emitted from an organic electroluminescencedevice for blue light emission into red color (R) and green color (G)through a fluorescent dye layer.

EXAMPLES

The present invention will next be described by way of Examples, whichshould not be construed as limiting the present invention thereto.

Example 1-1

Powder of compound 1 (host material) having the following StructuralFormula and powder of compound 2 (phosphorescent light-emittingmaterial) having the following Structural Formula were thoroughly mixedtogether at a ratio by mass of 30 70 (compound 1 compound 2). Theresultant mixture was pressure-molded in vacuum while heated to 150° C.,to thereby produce a light emitting layer-forming solid material as apellet of 1 g.

Compound 2 is a phosphorescent light-emitting material that emits whitelight by itself, that emits light at an emission peak of 468 nm, andthat exhibits a broad association emission at a peak of around 625 nm,when its concentration (dopant) is increased.

Next, the light emitting layer-forming solid material produced inExample 1-1 was used to produce an organic electroluminescent device asfollows.

—Production of Organic Electroluminescent Device—

A glass substrate (thickness: 0.5 mm, 2.5 cm×2.5 cm) was placed in awashing container, where the glass substrate was ultrasonically washedwith a neutral detergent and then ultrasonically washed in pure water,followed by thermal treatment at 120° C. for 120 min. Thereafter, thethus-treated glass substrate was UV-ozone treated for 30 min. Thefollowing layers were evaporated on this glass substrate by a vacuumevaporation method. Notably, in Examples and Comparative Examples,unless otherwise specified, the evaporation rate was 0.2 nm/sec. Theevaporation rate was measured with a quartz crystal unit. Also, thelayer thicknesses given below were measured with a quartz crystal unit.

First, ITO (Indium Tin Oxide) was evaporated on the glass substrate by avacuum evaporation method so as to form an anode having a thickness of100 nm.

Next, 4,4′,4″-tris(N,N-(2-naphthyl)-phenylamino)triphenylamine (2-TNATA)having the following Structural Formula doped with F4-TCNQ having thefollowing Structural Formula at 1% by mass was evaporated on the anode(ITO) by a vacuum evaporation method so as to form a hole injectionlayer having a thickness of 45 nm.

Next, α-NPD (bis[N-(1-naphthyl)-N-phenyl]benzidine) was evaporated onthe hole injection layer by a vacuum evaporation method so as to form ahole transport layer having a thickness of 7 nm.

Next, compound 7 having the following Structural Formula was evaporatedin vacuum on the hole transport layer so as to form a second holetransport layer having a thickness of 3 nm.

Next, the solid material produced in Example 1-1 was charged in anevaporation cell and then evaporated in vacuum on the second holetransport layer, to thereby form a light emitting layer having athickness of 30 nm.

Notably, the heating temperature of the evaporation source (evaporationcell temperature) was controlled to be 270° C. upon formation of thelight emitting layer through evaporation in vacuum.

The composition by mass of the light emitting layer at this stage wasmeasured by analyzing an evaporation film produced under the sameconditions through high-performance liquid chromatography (HPLC)(LC-2010HT, product of Shimadzu Corporation). As a result, the lightemitting layer was identified to have a ratio by mass (compound1:compound 2) of 60:40.

The evaporation conditions for the light emitting layer are as follows.

-   Evaporation apparatus: product of ALS Co., E-200-   Evaporation source container: alumina crucible (height: 10 mm,    diameter: 10 mm)-   Substrate temperature: 30° C.-   Heating temperature of evaporation source (evaporation cell    temperature): 270° C.-   Evaporation source-substrate interdistance: 40 cm-   Angle formed between the perpendicular line to the substrate surface    and the straight line connecting the evaporation source with the    substrate surface: 20° to 25°-   Degree of vacuum during evaporation: 1×10⁻⁵ Pato 3×10⁻⁵ Pa-   Evaporation rate: 0.2 nm/s

Next, BAlq(bis-(2-methyl-8-quinolinolato)-4-(phenyl-phenolate)-aluminuma(III))having the following Structural Formula was evaporated in vacuum on thelight-emitting layer so as to form an electron transport layer having athickness of 30 nm.

Next, LiF was evaporated in vacuum on the electron transport layer so asto form an electron injection layer having a thickness of 0.1 nm.

Next, a patterned mask (with which the formed emission regions were each2 mm×2 mm) was placed on the electron injection layer, followed byvacuum evaporation of metal aluminum, to thereby form a cathode having athickness of 70 nm.

The thus-obtained laminate was placed in a glove box which had beenpurged with nitrogen gas, and then was sealed in a stainless steelsealing can using a UV-ray curable adhesive (XNR5516HV, product ofNagase-CIBA Ltd.). Through the above procedure, an organicelectroluminescent device of Example 1-1 was produced.

The layer structure of the organic electroluminescent device of Example1-1 is as follows. The values in parentheses are the thicknesses of thelayers. <ITO (100 nm)/2-TNATA+1% by mass F4-TCNQ (120 nm)/α-NPD (7nm)/compound 7 (3 nm)/light emitting layer (30 nm)/BAlq (30 nm)/LiF (0.1nm)/Al (70 nm)>

When the light emitting layer-forming solid material of Example 1-1 isused, the number of evaporation sources required is one although twoevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 1-2

The procedure of Example 1-1 was repeated, except that the evaporationcell temperature upon evaporation for the light emitting layer waschanged from 270° C. to 280° C., to thereby produce an organicelectroluminescent device of Example 1-2.

In the same manner as in Example 1-1, the composition by mass of thelight emitting layer at this stage was measured by analyzing anevaporation film produced under the same conditions. As a result, thelight emitting layer was identified to have a ratio by mass (compound 1compound 2) of 50:50.

When the light emitting layer-forming solid material of Example 1-2 isused, the number of evaporation sources required is one although twoevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 2-1

Powder of compound 3 having the following Structural Formula (hostmaterial) and powders of the three light-emitting materials; i.e.,compound 4 having the following Structural Formula (blue phosphorescentlight-emitting material), compound 5 having the following StructuralFormula (green phosphorescent light-emitting material) and compound 6having the following Structural Formula (red phosphorescentlight-emitting material) were thoroughly mixed together at a ratio bymass of 86.5:12.0:1.1:0.4 (compound 3:compound 4:compound 5:compound 6).The resultant mixture was pressure-molded in vacuum while heated to 200°C., to thereby produce a light emitting layer-forming solid material asa pellet of 1 g:

Next, the light emitting layer-forming solid material produced inExample 2-1 was used in the same manner as in Example 1-1, to therebyproduce an organic electroluminescent device.

The evaporation cell temperature was controlled to be 270° C. uponformation of the light emitting layer through evaporation in vacuum. Inthe same manner as in Example 1-1, the composition by mass of the lightemitting layer at this stage was measured by analyzing an evaporationfilm produced under the same conditions. As a result, the light emittinglayer was identified to have a ratio by mass (compound 3:compound4:compound 5:compound 6) of 85.0:13.5:1.0:0.5.

The layer structure of the organic electroluminescent device of Example2-1 is as follows. The values in parentheses are the thicknesses of thelayers. <ITO (100 nm)/2-TNATA+1% by mass F4-TCNQ (120 nm)/α-NPD (7nm)/compound 7 (3 nm)/light emitting layer (30 nm)/BAlq (30 nm)/LiF (0.1nm)/Al (70 nm)>

When the light emitting layer-forming solid material of Example 2-1 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 2-2

The procedure of Example 2-1 was repeated, except that the evaporationcell temperature upon evaporation for the light emitting layer waschanged from 270° C. to 280° C., to thereby produce an organicelectroluminescent device of Example 2-2.

In the same manner as in Example 1-1, the composition by mass Of thelight emitting layer at this stage was measured by analyzing anevaporation film produced under the same conditions. As a result, thelight emitting layer was identified to have a ratio by mass (compound3:compound 4:compound 5:compound 6) of 84.5:14.0:0.9:0.6.

When the light emitting layer-forming solid material of Example 2-2 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 3-1

The procedure of Example 2-1 was repeated, except that SiC powder(highly thermally conductive material having no sublimation property)was additionally used as a light emitting layer-forming material andmixed together with compounds 3 to 6 at a ratio by mass of compound3:compound 4:compound 5:compound 6:SiC of 42.5:6.7:0.5:0.3:50.0,followed by pressure-molding in vacuum with heating to 200° C., tothereby produce a light emitting layer-forming solid material as apellet of 2 g.

Next, the light emitting layer-forming solid material produced inExample 3-1 was used in the same manner as in Example 1-1, to therebyproduce an organic electroluminescent device. The evaporation celltemperature upon vacuum evaporation for the light emitting layer wascontrolled to 265° C. The composition by mass of the light emittinglayer at this stage was measured by analyzing an evaporation filmproduced under the same conditions as follows. Specifically, the organicmaterials of the evaporation film were analyzed in the same manner as inExample 1-1 while the inorganic material thereof was analyzed with anICP mass spectrometer (ICPM-8500, product of Shimadzu Corporation). As aresult, the light emitting layer was identified to have a ratio by mass(compound 3:compound 4:compound 5:compound 6:SiC) of85.0:13.5:1.0:0.5:0.0 (not detected).

When the light emitting layer-forming solid material of Example 3-1 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 3-2

The procedure of Example 3-1 was repeated, except that the evaporationcell temperature upon evaporation for the light emitting layer waschanged from 265° C. to 275° C., to thereby produce an organicelectroluminescent device of Example 3-2. In the same manner as inExample 3-1, the composition by mass of the light emitting layer at thisstage was measured by analyzing an evaporation film produced under thesame conditions. As a result, the light emitting layer was identified tohave a ratio by mass (compound 3:compound 4:compound 5:compound 6:SiC)of 84.9:13.6:1.0:0.5:0.0 (not detected).

When the light emitting layer-forming solid material of Example 3-2 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 4-1

Compound 8 having the following Structural Formula (host material) andthe following light-emitting materials; i.e., compound 9 (bluefluorescent light-emitting material), compound 10 (green fluorescentlight-emitting material) and compound 11 (red fluorescent light-emittingmaterial) were thoroughly mixed together at a ratio of 94.5:4.7:0.6:0.2(compound 8:compound 9:compound 10:compound 11), followed bypressure-molding in vacuum with heating to 200° C., to thereby produce alight emitting layer-forming solid material as a pellet of 1 g.

Next, the light emitting layer-forming solid material produced inExample 4-1 was used in the same manner as in Example 1-1, to therebyproduce an organic electroluminescent device. The evaporation celltemperature upon vacuum evaporation for the light emitting layer wascontrolled to be 230° C. In the same manner as in Example 1-1, thecomposition by mass of the light emitting layer at this stage wasmeasured by analyzing an evaporation film produced under the sameconditions. As a result, the light emitting layer was identified to havea ratio by mass (compound 8:compound 9:compound 10:compound 11) of94.3:5.0:0.5:0.2.

The layer structure of the organic electroluminescent device of Example4-1 is as follows. The values in parentheses are the thicknesses of thelayers. <ITO (100 nm)/2-TNATA+1% by mass F4-TCNQ (120 nm)/α-NPD (7nm)/compound 7 (3 nm)/light emitting layer (30 nm)/BAlq (30 nm)/LiF (0.1nm)/Al (70 nm)>

When the light emitting layer-forming solid material of Example 4-1 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Example 4-2

The procedure of Example 4-1 was repeated, except that the evaporationcell temperature upon evaporation for the light emitting layer waschanged from 230° C. to 240° C., to thereby produce an organicelectroluminescent device of Example 4-2. In the same manner as inExample 1-1, the composition by mass of the light emitting layer at thisstage was measured by analyzing an evaporation film produced under thesame conditions. As a result, the light emitting layer was identified tohave a ratio by mass (compound 8:compound 9:compound 10:compound 11) of94.1:5.3:0.4:0.2.

When the light emitting layer-forming solid material of Example 4-2 isused, the number of evaporation sources required is one although fourevaporation sources have conventionally been required, and alsocumbersome co-evaporation can be avoided, which is advantageous.

Notably, in this Example, a hole injection layer consisting of 2-TNATA(99% by mass) and dopant F4-TCNQ (1% by mass) was formed by aco-evaporation method. The hoel injection layer may also be formed froma pellet of 2-TNATA and F4-TCNQ mixed together. As a result, the numberof evaporation sources required is one although two evaporation sourceshave conventionally been required, and also cumbersome co-evaporationcan be avoided, which is advantageous.

<Sublimation Temperature of Compound>

The sublimation temperature of each of compounds 1 to 11 used forforming the light emitting layer-forming solid materials refers to atemperature at which the mass of each compound is decreased by 10% bymass when measured in vacuum through TG-DTA (DTG-60, product of ShimadzuCorporation) under the following conditions: temperature increasingrate: 2° C./min and degree of vacuum upon is initiation of themeasurement: 10⁻² Pa. The results are shown in Table 1.

TABLE 1 Sublimation Compound temperature (° C.) Host material 1 200Phosphorescent light-emitting 2 255 material Host material 3 249Phosphorescent light-emitting 4 245 material Phosphorescentlight-emitting 5 251 material Phosphorescent light-emitting 6 243material Host material 8 218 Fluorescent light-emitting material 9 200Fluorescent light-emitting material 10 220 Fluorescent light-emittingmaterial 11 211

As shown in Table 1, since the sublimation temperatures of compounds 1and 2 used in Examples 1-1 and 1-2 are greatly different from eachother, the compositional ratios of the evaporation films could begreatly changed (adjusted) by changing the evaporation cell temperature.

In Examples 4-1 and 4-2, since the differences in sublimationtemperature between compounds 8, 9, 10 and 11 are within 20° C. as anabsolute value, the compositional ratios of the evaporation films couldnot be greatly changed by changing the evaporation cell temperature.

In Examples 2-1, 2-2, 3-1 and 3-2, since the differences in sublimationtemperature between compounds 3, 4, 5 and 6 are within 10° C. as anabsolute value, the compositional ratios of the evaporation films werechanged to a less extent than in Examples 4-1 and 4-2 even by changingthe evaporation cell temperature.

In conclusion, depending on the intended purpose, by combining togethermaterials whose sublimation temperatures are greatly or slightlydifferent, the extent of a change in the compositional ratio by mass ofthe formed evaporation film could be controlled by changing the heatingtemperature of the evaporation source (evaporation cell temperature).

<Evaluation> Examples 1-1 to 4-2

Ten organic electroluminescent devices were continuously produced underthe conditions of each of Examples 1-1 to 4-2. The thus-produced 10organic electroluminescent devices were evaluated as follows forexternal quantum efficiency, half service life, average value anddeviation. The results are shown in Table 2.

Comparative Examples 1-1 to 4-2

In each of Comparative Examples 1-1 to 4-2, the procedure of thecorresponding Example was repeated, except that the light emittinglayer-forming solid material was changed to conventional powdermaterials, which were evaporated by a co-evaporation method under theconditions that an evaporation film having the same composition wasobtained, to thereby produce 10 organic electroluminescent devices. Thethus-produced 10 organic electroluminescent devices were evaluated asfollows for external quantum efficiency, half service life, averagevalue and deviation. The results are shown in Table 2.

<<External Quantum Efficiency>>

Using source measure unit model 2400 (product of product of KeithleyInstruments Inc.), DC current of 10 mA/cm² was applied to each devicefor light emission. The brightness upon light emission was measured witha brightness meter BM-8 (product of TOPCON CORPORATION). The emissionspectrum and emission wavelength were measured with a spectrum analyzerPMA-11 (product of Hamamatsu Photonics K.K.). On the basis of theobtained values, the external quantum efficiency was calculated by abrightness conversion method.

<<Half Service Life (Drive Durability)>>

A constant current of 10 mA/cm² was applied to each organicelectroluminescent device, and the time required that the initialbrightness was decreased by half was measured.

TABLE 2 External quantum Half service Evaporation cell efficiency (%)life (h) temperature (° C.) 10 mA/cm² 10 mA/cm² Comp. Ex. 1-1 — 12.0 ±2.4 1200 ± 120 Ex. 1-1 270 15.0 ± 1.6 1850 ± 80  Comp. Ex. 1-2 — 10.2 ±2.1 1050 ± 110 Ex. 1-2 280 12.0 ± 1.1 1530 ± 70  Comp. Ex. 2-1 — 10.1 ±2.5  700 ± 170 Ex. 2.1 270 12.9 ± 1.2 1400 ± 100 Comp. Ex. 2-2 —  9.7 ±2.6  670 ± 150 Ex. 2-2 280 12.6 ± 1.3 1370 ± 90  Comp. Ex. 3-1 — 10.1 ±2.5  700 ± 170 Ex. 3-1 265 14.1 ± 0.7 1700 ± 80  Comp. Ex. 3-2 —  9.7 ±2.6  670 ± 150 Ex. 3-2 275 14.0 ± 0.6 1680 ± 80  Comp. Ex. 4-1 —  3.7 ±0.5 2200 ± 500 Ex. 4-1 230  4.2 ± 0.3 2450 ± 170 Comp. Ex. 4-2 —  3.6 ±0.6 2100 ± 450 Ex. 4-2 240  4.0 ± 0.4 2300 ± 150

As shown in Table 2, in Example 3-1, the evaporation film having acompositional ratio similar to that in Example 2-1 could be formed at anevaporation cell temperature lower by 5° C. than in Example 2-1, sincethe thermally conductive material was additionally used. As a result,reduction of thermodecomposition of the materials could be attained andthe drive durability (half service life) of the organicelectroluminescent device could be improved.

As compared with the organic electroluminescent devices of Examples 4-1and 4-2 in which the fluorescent light-emitting material was used, theorganic electroluminescent devices of Examples 1-1, 1-2, 2-1, 2-2, 3-1and 3-2, in which the phosphorescent light-emitting material was used,were found to exhibit higher improvement effect on drive voltage (halfservice life) than those of the corresponding Comparative Examples(which were produced through co-evaporation of the powder materials).That is, the improvement effect was about 1.1 times in use of thefluorescent light-emitting material, while the improvement effect wasabout 1.5 times to 2 times in use of the phosphorescent light-emittingmaterial. As compared with Comparative Examples in which co-evaporationwas performed, the deviations of the characteristics (emissionefficiency and half service life) of the organic electroluminescentdevices produced in Examples was decreased to about ⅔ to about ⅓.

Moreover, in Examples 3-1 and 3-2 in which the thermally conductivematerial was additionally used, the deviations of the characteristicswere further decreased and also the characteristics (emission efficiencyand half service life) were improved. This is likely becausethermodecompostion of the materials during evaporation could besuppressed.

The organic electroluminescence device containing the light emittinglayer produced from the light emitting layer-forming solid material ofthe present invention can be suitably used in, for example, displaydevices, displays, backlights, electrophotography, illuminating lightsources, recording light sources, exposing light sources, reading lightsources, markers, interior accessories and optical communication.

1. A light emitting layer-forming solid material, comprising: at leastone host material, and at least one light-emitting material, wherein thelight emitting layer-forming solid material is used for forming a whitelight emitting layer having a single layer structure by an evaporationmethod.
 2. The light emitting layer-forming solid material according toclaim 1, wherein the at least one light-emitting material is at leasttwo light-emitting materials.
 3. The light emitting layer-forming solidmaterial according to claim 2, wherein the at least two light-emittingmaterials emit different lights.
 4. The light emitting layer-formingsolid material according to claim 1, wherein the at least onelight-emitting material is a phosphorescent light-emitting material. 5.The light emitting layer-forming solid material according to claim 1,wherein a difference between a sublimation temperature of the hostmaterial and a sublimation temperature of the light-emitting material iswithin 20° C. as an absolute value.
 6. The light emitting layer-formingsolid material according to claim 1, wherein a difference between asublimation temperature of the host material and a sublimationtemperature of the light-emitting material is within 10° C. as anabsolute value.
 7. The light emitting layer-forming solid materialaccording to claim 1, further comprising at least one thermallyconductive material having no sublimation property, and thermalconductivity of the thermally conductive material is higher than that ofthe other materials contained in the light emitting layer-forming solidmaterial.
 8. The light emitting layer-forming solid material accordingto claim 1, wherein the light emitting layer-forming solid material isused as an evaporation source to form an evaporation film, and acomposition of the evaporation film is changed depending on a heatingtemperature of the evaporation source.
 9. The light emittinglayer-forming solid material according to claim 8, wherein thecomposition of the evaporation film is adjusted by controlling theheating temperature of the evaporation source.
 10. The light emittinglayer-forming solid material according to claim 1, wherein the lightemitting layer-forming solid material is evaporated to form anevaporation film whose composition is different from a composition ofthe light emitting layer-forming solid material.
 11. A method forproducing an organic electroluminescent device, comprising: evaporatinga light emitting layer-forming solid material so as to form a lightemitting layer, wherein the light emitting layer-forming solid materialcomprises at least one host material and at least one light-emittingmaterial, and wherein the light emitting layer is a white light emittinglayer having a single layer structure.
 12. An organic electroluminescentdevice obtained by a method comprising: evaporating a light emittinglayer-forming solid material so as to form a light emitting layer,wherein the light emitting layer-forming solid material comprises atleast one host material and at least one light-emitting material, andwherein the light emitting layer is a white light emitting layer havinga single layer structure.